14) 



This sub-genus characterizes the Upper. Etcheminian Fauna. 



The following is the original description of the species as published in 

 Bulletin XX. of the Natural History Society o New Brunawick. 



PAL.EOBOLUS BEETONENSIS. PI. IX., figs. 2a to h. 



" Oblately orbicular. Valves evenly rounded from the centre, except Palseobolus 

 that the borders are flattened at the sides and front. Both dorsal and feTadbedT 

 ventral valves somewhat pointed at the umbo, which is depressed in both 

 valves. Interior oj the ventral. This has a broad hinge area and a trian- 

 gular pedicle groove. The visceral cavity has two pairs of diverging 

 ridges, which mark the advance of the lateral muscles during the growth 

 of the shell. Between the outer and the inner pair originate the vascular 

 trunks, which in going forward throw off branches at an acute angle. 

 Interior of the dorsal valve. This valve has a broad, transversely striated 

 hinge area. The visceral cavity is traversed by two pairs of diverging 

 ridges, more widely divergent than those of the ventral valve ; there is 

 also a strong median septum along the middle of the valve. The central 

 group of muscle scars are about a fifth from the front of the valve. 



" Sculpture. The whole outer surface, except close to the umbo, is 

 ornamented with sharp concentric ridges which occasionally anastomose ; 

 these ridges have fine, faintly marked, radiating strite on their posterior 

 slopes, and are obscurely crenulated along their crests. 



"Size. Length 15 mm., width 17 mm. Dorsal valve somewhat 

 shorter than the ventral." [Bull. Nat. Hist. Soe. N.B., Vol. IV., p. 

 202,] 



The following are further particulars regarding this species. 



Ventral interior. The two pairs of diverging ridges extend across the Further 

 posterior third of the valve; of these the outer pair divide off the pos- this s'pecS. 

 terior lateral muscles, and the inner pair are directed toward the point of 

 attachment of the anterior laterals, to which they sometimes extend as 

 a border to the central callus ; in front of the callus on each side is a 

 depression, marking the place of the central group of muscle scars. The 

 vascular trunks in this valve run forward with a weak curve nearly to 

 the front of the valve ; the space between the trunks is about equal to 

 one third of the width of the valve ; beside the outer branches of the vas- 

 cular trunks referred to above, traces of internal branches are also found 

 towards the front of the valve. 



Dorsal interior. Of the two pairs of diverging ridges that traverse the 

 posterior third of the visceral cavity, the outer are longer than the inner ; 



